During experimental studies vertebrate cells need to be maintained at 33-37O C and there are a number of devices that have been designed to effectively accomplish this task. However, some experimental conditions require that the temperature of the cell be rapidly and reversible dropped to 10O C or lower. For example, the method of choice for disassembling and then reassembling the microtubules in many cells is reversible temperature shocks. During the last year we built a specimen temperature controller based on Peltier technology. This device sits on the stage of a light microscope and surrounds the Rose or perfusion chambers that we used for live-cell experimentations. It allows the temperature of a culture to be rapidly dropped from 37 to 10oC in less than 90 seconds, and to 4oC in about 3 min. The culture can then be warmed from these temperatures in approx. half-the cooling time. Since installing this device on our GFP imaging system, many have commented on its utility to their work. As a result we are preparing a manuscript describing how it is fabricated and used during the course of our work.